Tool head and method for machining a metallic workpiece

ABSTRACT

A tool head includes an ovoid basic element disposed about a center axis, at least two chip grooves formed in the basic element, and a number of major cutting edges. Each major cutting edge is disposed in a convex course along a respective chip groove of the at least two chip grooves. The major cutting edges define with their radially outermost region a nominal diameter. A radial distance from each major cutting edge to the center axis in a front, tip-side, arc portion increases up to the nominal diameter and in a rear, shank-side, arc portion decreases back down to a minimum diameter.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention relate to a tool head, inparticular to a drilling head for machining a metallic workpiece,wherein the tool head has a center axis and at least two major cuttingedges, which, viewed in a side view, take a convex course and definewith their radially outermost region a nominal radius. Embodiments ofthe present invention further relate to a method for machining ametallic workpiece with a tool bearing such a tool head.

2. Background Information

In machine cutting, in particular in the drilling of hard materials,there is generally the problem of high load upon the cutting edges ofthe tool head. This usually has the result that only comparatively lowmachining rates can be set and/or a high level of wear occurs. Thegenerated forces also occasionally lead under adverse conditions tochipping of the cutting edges.

Such problems arise in particular, for instance, in the aviation sector,in which very hard metallic materials, for instance titanium, are used.This situation is aggravated by the fact that drill holes are often madewith the aid of manually operated drilling tools.

In the case of the material titanium, there is the particular problemthat the chips tend to adhere or stick to the cutting edge. Succeedingcuttings can then lead to a locally very high load upon the cuttingedge, so that the risk of chipping is high. Accordingly, only low feedrates can be achieved.

The cutting edge geometry of a drill can have a substantial influence onthe cutting load upon the cutting edges. In a drilling head there areusually provided at least two major cutting edges, which are typicallyconnected to one another by a chisel edge. The cutting edges run roughlyradially outward and merge at a cutting corner typically into a minorcutting edge, which is continued along a chip groove in the axialdirection.

Moreover, high loads also arise in respect of cast materials, forinstance gray cast iron, in particular due to an inhomogeneous materialstructure.

EP 1 622 735 B1 discloses a drilling tool, developed specifically forthe machining of cast materials, in which the major cutting edges run ina convexly curved course and subsequently, at their radially outermostpoint, merge into a drill back, with the formation of a bend region at acutting corner.

Further drilling tools having convexly curved cutting edges can bederived, for instance, from U.S. Pat. No. 1,309,706 and U.S. Pat. No.3,443,459.

SUMMARY OF THE INVENTION

Embodiments of the invention provide, among several benefits, a toolhead which is improved with regard to the tool life and/or machiningrate, in particular a drilling head for machining hard materials, inparticular hard metals, such as titanium, or cast materials.

As one aspect of the present invention, a tool head is provided. Thetool head has at least two major cutting edges, which take a convexcourse, define with their radially outermost region a nominal radius,and to which a chip groove is respectively assigned. The tool head ismarked overall by a three-dimensional, ovoid basic shape, along which,on the one hand, the major cutting edges run and into which, on theother hand, the chip grooves are formed. The ovoid basic shape is herecharacterized in that a radial distance of the major cutting edges tothe center axis, in a front tip-side arc portion, increases up to anominal diameter, and then, in a rear shank-side arc portion, decreasesback down to a minimum diameter.

As a result of the distinct ovoid shape, the forces, in the machinecutting of a workpiece made of a hard material, in particular titanium,hard metal or cast material, are transmitted and conducted in aparticularly advantageous manner along the ovoid surface of the drillinghead, so that, all in all, a significantly lesser load upon the cuttingedges is achieved. Studies have shown that, with an ovoid basic shape ofthis type, significantly higher cutting speeds and feed rates comparedto traditional drilling tools can be obtained.

Of particular importance in this context is the tapered region in theshank-side arc portion, so that the major cutting edges do not end in acutting edge corner or merge at their nominal diameter into a minorcutting edge, as is customary in traditional drills also having convexlycurved cutting edges. The tool head is therefore free from minor cuttingedges which run along the chip grooves.

The tool head is therefore overall marked by convexly curved majorcutting edges, which, in the rear shank-side portion, shrink back to theminimum radius. The major cutting edges are respectively adjoined in theperipheral direction by a surface segment, in the form of a flank, ofthe ovoid basic element, which surface segment tapers to the followingchip groove.

In accordance with the ovoid basic shape, the front arc portionpreferably has a greater axial length than the rear arc portion, i.e.,the axial distance of the region of greatest diameter (nominal diameter)to the foremost point of the tool head is greater than the axialdistance between the region of nominal diameter up to the shank-side endof the major cutting edge. In particular, the front arc portion here hasan axial length which is greater, by a factor of 1.5 to 2 times,compared to the rear arc portion.

Furthermore, the minimum diameter preferably corresponds to 0.9 to 0.7times the nominal diameter. As a result of the reduced diameter in theshank-side region of the tool head, a certain clearance is obtained,which—in addition to the particularly advantageous force transmission—isof particular advantage also with regard to withdrawal from a drillhole.

In addition, the rear arc portion is here expediently more stronglycurved than the front arc portion. As a result, the axial length whichis necessary in total is kept low, in combination with good forcetransmission.

The entire drilling head, that is to say the axial length of the majorcutting edges, preferably has an axial length in the direction of thecenter axis which lies within the range of 0.8 times to 1.5 times thenominal diameter.

Preferably, the individual arc portions are, in turn, preferablythemselves composed of a multiplicity of individual segments havingdifferent radii. This enables, on the one hand, the advantageous anddesired ovoid shape to be realized. At the same time, through a suitablechoice of individual radii of the segments, an optimized forcetransmission is obtained, so that the cutting load is kept low overall.Expediently, the radii of the segments of the front arc portion herepreferably steadily increase in the direction of the rear arc portionand, furthermore, the radii of the segments of the rear arc portionpreferably steadily decrease again, starting from the front arc portion.In the region of nominal radius, the major cutting edge therefore hasthe greatest radius and thus the least curvature.

The major cutting edges are preferably connected to one another on theend face by a chisel edge. In particular, in the region of the chiseledge, a pointing is introduced.

In an expedient embodiment, the tool head has in the region of thechisel edge a traditional point grinding, in particular, for instance, aconical grinding. The central drill bit region is therefore configuredin the style of a traditional drill bit, so that a good centeringfunction is ensured. The point grinding extends in the radial directionpreferably merely over a diameter corresponding to 0.05 times to 0.1times the nominal diameter. As a result of this overall very small pointgrinding, a centering point is substantially configured.

The major cutting edges run, all in all, roughly helically along thesurface of the ovoid basic element. Correspondingly hereto, the chipgrooves also run spirally.

The tool head is preferably configured as a reversibly exchangeable toolhead and is therefore designed for so-called modular carrier tools, inwhich a respective tool head is inserted into a corresponding receptacleof a carrier. The tool head is here preferably overall configured in onepiece from a monolithic basic element, in which the chip grooves areintroduced, and the major cutting edges are configured by a grindingprocess. The tool head has a coupling pin for insertion into areceptacle of the carrier. Expediently, this is configured forreversible and, in particular, tool-less insertion into the receptacleof the carrier.

Overall, the rear arc portion of the major cutting edges is adjoined bya shank region, which, in the case of the modular carrier tool, isformed by the carrier, wherein the diameter of the shank region issmaller than or equal to the minimum diameter. The shank regiontherefore has no guiding or cutting function. These functions areperformed solely and completely by the ovoid tool head.

With the tool head which is described here, having the substantiallyovoid basic shape, significantly higher cutting speeds compared totraditional tools can be obtained in respect of hard metals, inparticular titanium. Thus the maximum cutting speed in the use oftraditional drilling heads, for instance having normal conical grinding,is maximally VC=20 m/min. at a feed rate of F=0.05 mm/revolution.Studies have now shown that, with the tool head which is described here,the cutting speed was able to be doubled to VC=40 m/min., with the sameor even improved drilling results, and the feed rate/revolution waslikewise able to be significantly increased, for instance to values ofF=0.12 to 0.15.

Accordingly, in the inventive method for machining a hard metallicmaterial, in particular titanium, a cutting speed of 30 m/min. or moreis also preferably set. Moreover, a feed rate within the range fromF>0.1 to, for instance, F=0.5 is set. Preferably, at the cutting speedof VC=about 40 m/min., a feed rate of about 0.15 mm/revolution (in thecase of a double-edged tool) is set.

The particular advantage of the ovoid shape which is presented here isthe diversion and transmission of the cutting forces and of the cuttingpressure via the surface into the shank of the carrier, so that, all inall, the load upon the tool head is reduced.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Novel features and characteristics of the disclosure are set forth inthe appended claims. The disclosure itself, however, as well as apreferred mode of use, further objectives and advantages thereof, willbest be understood by reference to the following detailed description ofan illustrative embodiment when read in conjunction with theaccompanying figures. One or more embodiments are now described, by wayof example only, with reference to the accompanying figures wherein likereference numerals represent like elements and in which:

FIG. 1 shows a side view of a modular carrier tool having a drillinghead;

FIG. 2 shows a side view of the carrier tool according to FIG. 1,rotated through 90° compared to the representation shown in FIG. 1;

FIG. 3 shows a side view of the drilling head inserted in the carriertool according to FIG. 1; and

FIG. 4 shows an end view of the drilling head according to FIG. 3.

The figures depict embodiments of the disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined features and technical advantages ofthe present disclosure in order that the detailed description of thedisclosure that follows may be better understood. Additional featuresand advantages of the disclosure will be described hereinafter whichform the subject of the claims of the disclosure. It should beappreciated by those skilled in the art that the conception and specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of thepresent disclosure. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the disclosure as set forth in the appended claims. The novelfeatures which are believed to be characteristic of the disclosure, bothas to its organization and method of operation, together with furtherobjects and advantages will be better understood from the followingdescription when considered in connection with the accompanying figures.It is to be expressly understood, however, that each of the figures isprovided for the purpose of illustration and description only and is notintended as a definition of the limits of the disclosure.

The example drilling tool 2 represented in FIGS. 1 and 2 is configuredas a modular carrier tool, which extends along a central longitudinalaxis 4 and has a carrier 6 and a drilling head 8 inserted therein. Thecarrier 6 is in turn divided into a rear shank region 10 and a front, inthe illustrative embodiment grooved, shank region. The rear shank region10 serves for clamping of the drilling tool 2 into a machine tool. Thefront shank region 12 has on the end face a receptacle 13 (FIG. 2), inwhich the drilling head 8 is exchangeably inserted with the aid of acoupling pin 14. The insertion is realized preferably without tools, byfirst inserting the drilling head 8 axially into the receptacle 13 andthen turning it, say, through 90°, for instance. An automatic centeringand clamping of the coupling pin 14 in the receptacle 13 is hereuponrealized.

In the illustrated example embodiment, the drilling head 8 is all in alla monolithic, one-piece drilling head, in particular a hard metal orsintered drilling head, which is formed by an ovoid basic element 16 inwhich chip grooves 18 are introduced. The chip grooves 18 arerespectively bounded by major cutting edges 20, which extend helicallyalong the surface of the basic element 16. Each of the major cuttingedges 20 is adjoined in the peripheral direction by a surface segment 22of the ovoid basic element 16, in the form of a flank. These segments 22extend in the peripheral direction respectively up to the followinggroove.

The two major cutting edges 20 are mutually connected in the centerregion by a chisel edge 24 (cf. FIG. 4). In the region of the chiseledge 24, the basic element 16 has a point grinding, for instance in thestyle of a conical taper. At the same time, a taper 26 is also providedin this region, in order to reduce the drill center in the region of thecenter edge 24. As can further be seen, in particular, from FIG. 4,coolant bores 28 are also additionally configured in the chip grooves18.

As can be seen, in particular, from FIG. 3, the drilling head 8 hasoverall a nominal diameter D. In addition, the drilling head has anaxial total length L, which reaches from the tip of the chisel edge 24up to a rear centering pin. In contrast, the major cutting edges 20extend merely over an axial length L1 up to a rear step, which is thenadjoined by the coupling pin 14. The nominal diameter D here correspondsroughly to the axial length L1.

The rear arc portion 30B tapers, starting from the nominal diameter D,back to a minimum diameter D_(min). Preferably, this lies roughly withinthe range of 0.9 to 0.7 times the nominal diameter D.

As can be seen, in particular, from the side view of FIG. 3, the convexcourse of the major cutting edges 20 is composed of a front arc portion30A and an adjoining rear arc portion 30B. The front arc portion 30Ahere extends up to the region having the greatest radial distance of therespective major cutting edge 20 to the central longitudinal axis 4,where the drilling head 8 assumes the nominal diameter D. Furthermore,with reference to FIG. 3, it can be seen that the rear arc portion 30Bhas a significantly stronger curvature following on from the front arcportion 30A. The dashed line depicted in FIG. 3 shows an imaginarycontinuation of the front arc portion 30A, with constant radius ofcurvature.

Due to the ovoid contour, the two arc portions 30A, 30B are composed ofa plurality of segments having different radii. The radii hererespectively increase to the region of nominal diameter D. Directly onthe tip in the region of the chisel edge, the two major cutting edges 20are oriented at a point angle α to each other, which angle, in theillustrative embodiment, lies at 140° and generally within the rangebetween, for instance, 130° and 150°.

The chisel edge 24, as the center region between the two major cuttingedges 20, has a comparatively small diameter d, which preferably liesmerely between 0.05 to 0.1 times the nominal diameter D.

The here described ovoid basic geometry of the drilling head 8, havingthe convex, in particular helically guided major cutting edges 20, whichalso taper again in the rear arc portion 30B, so that no cutting edgecorner is configured, in conjunction with the introduced chip grooves 18and the segments 22, which latter are likewise arched, in particular, inaccordance with the ovoid surface contour, leads to a particularly goodforce and pressure transmission into the carrier 6. As a result, thecutting load is less, and higher feed rates, as well as higher cuttingspeeds, compared to traditional drilling heads 8 can be obtained.

The present invention has been described with reference to a modulardrilling tool having a double-edged drilling head, yet is not limitedhereto. Instead of a modular tool, a one-piece tool, in particular asolid-carbide tool, having the specific head geometry is alternativelyconfigured. In principle, the head geometry can also be used in othertools, for example milling tools. Finally, the head geometry can also beused in triple-edged or multi-edged tools. The cutting edges arepreferably configured, in particular by grinding, on the basic element,but alternatively can also be configured as separately fastened cuttinginserts or cutter bars.

The invention claimed is:
 1. A tool head comprising: an ovoid elementdisposed about a center axis; at least two chip grooves formed in theovoid element; a number of major cutting edges, each major cutting edgedisposed in a convex course along a respective chip groove of the atleast two chip grooves, the major cutting edges defining with theirradially outermost region a nominal diameter; and a shank region;wherein a radial distance from each major cutting edge to the centeraxis in a front, tip-side, arc portion increases up to the nominaldiameter and in a rear, shank-side, arc portion decreases back down to aminimum diameter; wherein the rear arc portion has a radius of curvaturesmaller than a radius of curvature of the front arc portion; and whereinthe shank region adjoins and directly abuts the rear arc portion of themajor cutting edges, the shank region having a diameter which is smallerthan the minimum diameter at the abutment between the shank region andthe rear arc portion.
 2. The tool head as recited in claim 1, whereinthe front arc portion has a greater axial length than an axial length ofthe rear arc portion.
 3. The tool head as recited in claim 2, whereinthe axial length of the front arc portion is greater than the axiallength of the rear arc portion by a factor of 1.5 to 2 times.
 4. Thetool head as recited in claim 1, wherein the minimum diametercorresponds to 0.9-0.7 times the nominal diameter.
 5. The tool head asrecited in claim 1, wherein the major cutting edges are connected to oneanother by a chisel edge and, in the region of the chisel edge, a taperis introduced.
 6. The tool head as recited in claim 5, comprising aconical taper in the region of the chisel edge.
 7. The tool head asrecited in claim 6, wherein the chisel edge has a diameter within therange up to 0.05-0.1 times the nominal diameter.
 8. The tool head asrecited in claim 1, wherein the major cutting edges run helically alongthe chip grooves.
 9. The tool head as recited in claim 1, wherein thetool head is configured as a exchangeable tool head and furthercomprises a coupling pin structured to be inserted into a receptacle ofa carrier.
 10. A method for machining a metallic workpiece with a toolhaving a tool head as recited in claim
 1. 11. The method as recited inclaim 10, wherein the method comprises machining the metallic workpieceat a cutting speed of 30 m/min.
 12. The method as recited in claim 11,wherein the metallic workpiece is formed from titanium or a high alloysteel.
 13. The method as recited in claim 10, wherein the methodcomprises machining the metallic workpiece at a feed rate of about 0.15mm/revolution.
 14. The tool head as recited in claim 1, wherein an axiallength of the tool head in the direction of the center axis is withinthe range of 0.8 times to 1.5 times the nominal diameter.